Mixtures of organic phosphonates and anionic polymers to improve acid extraction of uranium

ABSTRACT

A method of improving the acid leaching of uranium ores which comprises adding to such ores while they are being leached between 0.01-2 lb. per ton of a composition comprising: 
     a. aminotris methylene phosphonic acid, and 
     b. a water-soluble copolymer of vinyl sulphonic acid and acrylic acid combined in a weight ratio of from 2:1 to 1:2 and having a molecular weight within the range of from 500 to 100,000, 
     with the weight ratio of a:b being within the range of 1:2 to 2:1.

INTRODUCTION

In the processing of uranium-containing ores, they are ground and subjected to an acid leaching step. The most common acid leaching process is the so-called "acid process." This process is described in detail in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Volume 21, Inter-Science, 1970, page 13. As stated in this publication,

"Typical leach reactions are the following:

    6H.sub.2 SO.sub.4 +3MnO.sub.2 +3UO.sub.2 →3UO.sub.2 SO.sub.4 +3MnSO.sub.4 +6H.sub.2 O

    3H.sub.2 SO.sub.4 +NaClO.sub.3 +3UO.sub.2 →3UO.sub.2 SO.sub.4 +NaCl+3H.sub.2 O

"In practice, the oxidation potential of the solution is determined by measuring the ferric to ferrous ratio. The role of ferric iron in the oxidation of tetravalent uranium is important. The internal reaction that makes possible the two oxidation reactions illustrated above involves the conversion of ferrous iron to ferric iron. The ferric iron then oxidizes the UO₂. The reaction (7) is probably taking the following course:

    2Fe.sup.2+ +MnO.sub.2 +4H.sup.+ →2Fe.sup.3+ +Mn.sup.2+ +2H.sub.2 O

    UO.sub.2 +2Fe.sup.3+ →UO.sub.2.sup.2+ +2Fe.sup.2+

"In most ores, sufficient iron is present for this reaction. It is necessary to add metallic iron to some ores to ensure an adequate supply of iron."

THE INVENTION

A method of improving the acid leaching of uranium ores which comprises adding to such ores while they are being leached between 0.01-2 lb. per ton of a composition comprising:

a. aminotris methylene phosphonic acid, and

b. a water-soluble copolymer of vinyl sulphonic acid and acrylic acid combined in a weight ratio of from 2:1 to 1:2 and having a molecular weight within the range of from 500 to 100,000,

with the weight ratio of a:b being within the range of 1:2 to 2:1.

THE AMINOTRIS METHYLENE PHOSPHONIC ACID

This material is prepared by reacting ammonia, formaldehyde, and phosphorus acid. This reaction is described in detail in Irani, U.S. Pat. No. 3,288,846. When used in the invention, this phosphonate is most preferably in the form of one of its water-soluble salts, preferably its sodium salt. It is available commercially in the form of a 50% aqueous solution of its sodium salt.

THE ACRYLIC ACID VINYL SULPHONIC ACID COPOLYMER

These polymers are prepared by copolymerizing acrylic acid and vinyl sulphonic acid, particularly sodium vinyl sulphonate. These copolymers may have a weight ratio varying between 1:1 to 2:1 with a preferred ratio of acrylic acid to vinyl sulphonic acid being about 1:0.45. These copolymers are difficult to prepare from the standpoint of producing high molecular weight species thereof. They usually have molecular weights as low as 500 with molecular weights rarely exceeding 100,000. A preferred material has a molecular weight within the range of about 750 to about 50,000.

RATIO AND DOSAGE OF THE AMINOTRIS METHYLENE PHOSPHONIC ACID

The amount of aminotris methylene phosphonic acid in relation to the amount of acrylic acid vinyl sulphonate copolymer may vary on a weight basis between 2:1 to 1:2 with a preferred ratio being about 1:1.

These materials are used to treat uranium slurries at a dosage ranging from as little as 0.01-2 pounds per ton of slurry with a preferred dosage being within a range of 0.05-1 lb. per ton.

ILLUSTRATION OF THE INVENTION

Using a standard commercial ore, a composition having the following makeup was tested:

    ______________________________________                                         FORMULATION I                                                                  Ingredients          % by Weight                                               ______________________________________                                         Sodium salt of acrylic acid/                                                                        50                                                        vinyl sulfonate copolymer                                                      (25% in water)                                                                 50% solution of N(CH.sub.2 PO.sub.3 H.sub.2).sub.3                                                  25                                                        50% solution of sodium hydroxide                                                                    15                                                        water                10                                                        ______________________________________                                    

In the above composition, the ratio of vinyl sulphonate to acrylic acid was 0.45:1.

Using the formulation described above, two different types of uranium ores were tested in a leach cycle. Dosage rates were within 0.05 to 1.0 pounds per ton of ore.

Two-stage treatment was used beginning with 990 grams ore, 990 ml. H₂ O, 120 ml. core H₂ SO₄ giving a pH of about 1.5 at ambient temperatures and a U₃ O₈ head of 0.183-0.185 in original ore. The Second stage was treated with 402 ml. H₂ O, 135 ml. H₂ SO₄ for four hours at 275° F. under 60 PSI using air pressure.

    ______________________________________                                                      % U.sub.3 O.sub.8                                                                           Free                                                 Uranium Ore  Recovery     Acid      pH                                         ______________________________________                                         Type 1 (HD = 0.185)                                                            Control      89.19%       85.4 gpl  0.10                                       Formulation I                                                                               91.35%       88.1 gpl  0.07                                       (0.5 lb/ton)                                                                   Formulation I                                                                               91.35%       76.2 gpl  0.06                                       (0.5 lb/ton)                                                                   Type 2 (HD = 0.183)                                                            Control      92.90%       99.1 gpl  0.12                                       Formulation I                                                                               95.08%       101.3 gpl 0.05                                       (0.5 lb/ton)                                                                   Formulation I                                                                               94.54%       96.7 gpl  0.04                                       (0.5 lb/ton)                                                                   ______________________________________                                    

The tests for Type I ore gave below normal results, but it is still observed that using the formulation and composition of the invention dramatically improves the recovery of U₃ O₈ from the ore.

The tests on Type 2 uranium ore gave results for recovery per cent much more in line with normal observation. It is seen that, again, the use of the formultions of this invention dramatically improves the recovery of U₃ O₈ from the starting ores in this acid-leaching process. 

I claim:
 1. A method of improving the acid leaching of uranium ores which comprises adding to such ores while they are being leached between 0.01-2 lb. per ton of a composition comprising:a. aminotris methylene phosphonic acid, and b. a water-soluble copolymer of vinyl sulphonic acid and acrylic acid combined in a weight ratio of from 2:1 to 1:2 and having a molecular weight within the range of from 500 to 100,000,with the weight ratio of a:b being within the range of 1:2 to 2:1.
 2. The method of claim 1 where the ratio of a:b is 1:1 and the ratio of acrylic acid to vinyl sulphonic acid is 1:0.45. 